Overview

Traceable measurements of surface form and property are essential for controlling the use of or assessing the condition of machined parts and tools in high precision mechanical manufacturing machines especially when these components are subject to wear and surface contamination. Therefore, this project will develop new tactile microprobes for reliable and ultrafast, on-the-machine (i.e. in-line) topographical micro-form and roughness measurements that are 30 times faster than conventional methods and fast methods using contact resonance and force-distance curves to measure adhesion, stiffness, friction, coating thickness and to detect contaminants through adhesion contrast.

 

Need

Quality control for manufacturing machines is predominantly carried out off-line, and thus requires the workpiece to be dismounted, measured off-line, and then re-mounted. This is both time consuming and expensive and therefore on-the-machine, in-situ characterisation is urgently needed. Other challenging constraints for the measurement and quality control of machined parts include the size of the small micro-structures to be measured against the strong vibrations of the workpiece, contamination by oil and lubricants and large temperature variations. Fast optical sensors are not adequate for measuring such contaminated surfaces and large measurement artefacts can result.

Another measurement option is the use of tactile small coordinate measuring sensors i.e. microprobes. However, tactile microprobes are currently not small enough or fast enough for use in the quality control of manufacturing machines. Current, silicon microprobes with 5 mm long cantilevers with integrated silicon tips for roughness measurements in injection nozzles fulfil several requirements like high scanning speed and low probing force, but suffer from strong tip wear, reduced vertical measurement range and a lack of damping. Manufactured parts in industry are also becoming smaller and smaller (micro-metre size), leading to higher requirements concerning the uncertainty of topography and micro-form measurements (where an uncertainty of < 50 nm is required). However, precise measurements are only possible, if the influence of the probing tip shape on the measured profile can be appropriately corrected for.

Further to roughness and topography measurements there is a need in industry to simultaneously measure the mechanical properties of workpieces. Examples of surface layers needing to be measured simultaneously on-the-machine include rubber, polyurethane and wear protection coatings on printing rolls. In addition to the workpiece, a wide variety of tools on micro-finishing machines as well as on roll grinding machines and wear testers also need to be measured on-line.

 

Objectives

The project is focussed on the traceable measurement and characterisation of multifunctional ultrafast microprobes for integration into manufacturing machines. The specific objectives are

  1. To develop methods for i) obtaining wear resistant probing tips and to characterize the tips on-the-machine with an uncertainty ≤ 50 nm), ii) the development of the morphological filtering of the tip influence on measurements, iii) setting probing force and scanning speed of microprobes and iv) to develop prototype microprobes with integrated actor, preamplifier and damping for fast measurement of topographic micro-form, structure, roughness and enhanced surface properties like elasticity, adhesion, contamination and thickness of coatings.
  2. To develop new large deflection (> 200 µm) and high speed (> 10 mm/s) microprobes for simultaneous measurement of micro-form, roughness, elasticity, adhesion, contamination and thickness of coating layers under industrial conditions. This should include the development of i) pre-deflected cantilevers, ii) actively damped or material-damped cantilevers with thin-film piezoelectric or electro-thermal actuators and iii) thin-film piezoelectric actuator exciting higher-order bending modes suitable for fast CR measurements.
  3. To develop validated Contact Resonance (CR) and Force-Distance Curves (FDC) methods for the fast measurement of enhanced surface properties with microprobes on-the machine. The main aim for developing the CR method is the fast detection (< 10 s) of property contrasts on the surface of machined parts on-the-machine, including i) the development of a theoretical model, ii) the determination of the measurement range and resolution, iii) the determination of the lateral resolution, iv) the measurement of the thickness (10 nm – 1 µm) of soft coatings on hard substrates v) fast measurement of the stiffness and characterisation of the elastic modulus of machined parts on-the-machine and vi) the production of a Good Practice Guide. Aims of the FDC method are i) to detect liquid contamination layers from lubricants through adhesion contrast and extend the range of measurable thicknesses to 10 nm – 500 nm, ii) measurement of the stiffness and of the elastic modulus in the range 100 MPa – 3 GPa, iii) measurement of the thickness (1 - 200 nm) of soft coatings on hard substrates, iv) comparison of FDC results with CR results for a better understanding of the CR method, v) adhesion and friction measurements on the surface of machined parts, vi) to implement the method on-the-machine, vii) to improve the measurement speed and viii) to produce a Good Practice Guide.
  4. To develop the integration of microprobes into manufacturing machines, roll grinding machines and wear measuring machines and to develop measuring methods resistant against ambient influences. For the manufacturing machine, this will include i) the development of a new high-speed feed-unit, ii) the development of a probe-machine interface, iii) the development a high-speed data acquisition system and iv) the improvement of resistance against ambient influences. For the roll grinding machines, this will include i) the development of mechatronics to drive the microprobe into contact with the roll, ii) the development of a measurement strategy for roughness measurements, iii) measurements of microprobes with and without damping in comparison to reference probes and iv) the production of a Good Practice Guide. For the wear measuring machines, this will include i) the integration of the microprobes into a pin-on-disc tribometer, ii) the relative wear measurement by an additional reference microprobe, iii) the integration of the microprobes into a reciprocating tribometer and vi) the integration of an additional traverse unit to enable measurement of wear damage during in-situ measurements of wear and v) the production of a Good Practice Guide.
  5. To facilitate the take up of the developed technology and measurement infrastructure, in particular the methods for traceable microprobe measurements on-the-machine by the measurement supply chain.

 

Progress beyond the state of the art

The use of dimensional metrology on manufacturing machines is currently hindered by strong vibrations, contamination of workpieces and the high measurement speed requirements of the sensors. Existing piezoresistive silicon microprobes can be used for standard roughness measurements at high speeds up to 15 mm/s, but the wear of the silicon tips is so strong, that approximate only 1,000 measurements in the roughness range below Ra = 2 μm can be performed until the probe must be exchanged. In addition to the quick tip wear, these microprobes suffer from exhibiting no damping, a reduced measurement range of approximately 70 µm and contain no integrated actuator or preamplifier. The new microprobes to be developed by this project will contain wear resistant diamond tips, exhibit critical damping, an extended measurement range of more than ± 200 µm, and will be able to be operated either under critical damping or in resonance using an integrated actuator and a preamplifier on the printed circuit board (PCB).

The project will for the first time bring piezoresistive silicon microprobes onto manufacturing machines for ultrafast roughness, topography and micro-form measurements at measurement speeds up to 15 mm/s and vertical measurement ranges up to ± 200 µm. In order to obtain the small uncertainties in roughness measurements required (i.e. uncertainty for Ra = 3 %) the project will develop a microprobe unit (microprofiler) with integrated feed-unit for traverse speeds up to 15 mm/s. The biggest challenge when developing this, will be to measure roughness under strong vibration levels, high contamination levels and strong temperature variations.

For precise topography and micro-form measurements, the influence of the probing tip shape on the measured profiles needs to be corrected for. Thus, robust methods for measuring the probe tip shape on-the-machine will be developed. Several types of tip characterisation standard will be tested for ultrafast tip shape measurements. The project will develop algorithms for the evaluation of profile measurements and develop algorithms for morphological filtering of the profiles for the tip shape.

Several applications for microprobes exist where not only workpiece topography is needed, but where information about the mechanical properties of the measured material underneath the tip is also necessary. This applies to all kind of wear protective layers, including the layer thickness. The project will for the first time apply two methods simultaneously to topography measurements made with microprobes. The first method is fast contact-resonance (CR) measurements, well-known from Atomic Force Microscopy (AFM) metrology for the measurement of Young’s modulus (used to describe tensile elasticity), simultaneously with topography measurements. The project will go beyond the state of the art by developing a new type of actuator integrated into the microprobes for CR measurements. This new actuator will allow the selective excitation of high eigen frequencies (i.e. the frequency at which a system tends to oscillate in the absence of any driving or damping force) and thus will suppress noise and improve performance. The second method will be force-distance curve (FDC) measurement. The project will go beyond the state of the art by developing methods for the detection of lubricant layers on workpieces and the measurement of their thickness in a large range between 10 nm and 500 nm. Moreover, new test methods will be developed with both CR and FDC for the detection of contrasts due to different elastic moduli of sample components and/or to different thicknesses of coating layers.

Tribology includes the study of friction, lubrication, and wear of interacting surfaces. Current, real-time measurement of small wear volumes on tribological test systems use post-test static stylus profilometry or real time non-contact optical measurement. The project will go beyond this by the application of fast microprobe measurements in real time on tribological test systems.

 

Results

Expected results are:

  • New high-speed microprobes with large measurement range, pre-deflection, wear resistant probing tips, actively damped or material-damped cantilevers with thin-film piezoelectric or electro-thermal actuators and thin-film piezoelectric actuators exciting higher-order bending modes suitable for fast CR measurements.
  • A microprobe unit with integrated feed-unit for scanning speeds up to 10 mm/s
  • Methods for morphological filtering of the tip influence on measurements
  • Methods for setting probing force and scanning speed of microprobes for fast measurement of topographic micro-form, structure and roughness.
  • Validated CR and FDC methods for the fast measurement of enhanced surface properties with microprobes on-the machine, including
  • the development of a theoretical model for CR
  • the determination of the measurement range, resolution and the lateral resolution of CR
  • the measurement of the elastic modulus in the range 100 MPa – 3 GPa
  • the fast measurement of the stiffness, adhesion and friction on the surface of machined parts
  • the measurement of the thickness (10 nm – 1 µm) of soft coatings on hard substrates
  • the detection of liquid contamination layers from lubricants through adhesion contrast
  • comparison of FDC results with CR results for a better understanding of the CR method.

 

Impact

The project will support industry to integrate new tactile microprobes into their manufacturing machines. This will lead to benefits for high precision mechanical engineering, printing and surface foil industries, transportation, power generation, residential, passenger cars, trucks and buses, paper machines and the mining industries. Examples of specific impact include:

  • The development of new microprobe devices and prototypes for simultaneous roughness and modulus mapping measurements on-the-machine.Micro-finishing machine producers can use the developed microprofilers with integrated feed-units for roughness measurements. Manufacturers of high-tech roll measuring and control systems and, manufacturers of tribometers and other similar end-users will benefit from microprobes without feed-units for topography and CR measurements. These new microprobe devices will also be implemented into dimensional surface measuring machines, where ever AFM cantilever tips are too short. PTB will integrate the new probes into their measurement platform Profilscanner in order to provide traceable micro-form measurements and calibration of reference artefacts to end-users.
  • A new method for the tip form measurement on-the-machine.The beneficiaries will be micro-finishing machine producers, roll grinding machine producers and companies producing thin soft layers. Micro-Electro-Mechanical Systems (MEMS) manufacturers will benefit predominantly from the more reliable adhesion measurements and wear protection layer manufacturers will benefit from the improved friction measurements.
  • A new method for the determination of the maximum scanning speed at a given probing force.Developers of optical and tactile surface profile and roughness measuring instruments, microfinish machine manufacturers, roll measuring machine manufacturers, tribology measurement instrument manufacturers and similar organisations will benefit from these results.
  • Two new measurement methods: CR and FDC.Beneficiaries will be producers of functional coatings and micro- and nanotechnology industries including MEMS developers.
  • The development of new reference materials and calibration standards. Beneficiaries will be organisations interested in modulus mapping and those providing the microprobing systems. In the short-term BAM can supply the calibration and reference standards.